I'm not sure when I last saw a finale as brilliant and yet bleak as this. Two hours in which Birgitte Nyborg, the uncorruptable prime minister who forbade her spin doctor from smearing a rival, saw her ideals and her marriage crumble as she attempted to cling on to power. As she ushered Philip and the kids into the lift – having given a speech about fighting and living for all that you love – Birgitte was almost unrecognisable; no longer the loved-up idealist we encountered clocking off for her children's party five weeks ago.

Borgen has painted a skilful portrait of a woman whose political ambition arguably became more important than everything else: her marriage, her family, the friend who had supported her through everything, her ethics around press freedom. Even her face seemed to become harder as she became ever tougher. I found the final two hours in many ways a very difficult watch: like many other viewers I had rather fallen for Birgitte. I wanted her to work out her problems at home; I hoped she'd find a balance between being prime minister and life outside.

But it seemed to become increasingly clear that actually, she didn't want that. She lost perspective. Instead, she wanted power at almost all costs. (Bent? Birgitte. You really betrayed him?) Even when it seemed she didn't have a clear idea of what she wanted to do with that power – the scene with Kasper pressing her for ideas was a particularly clever one, I thought.

If we're being critical, it felt slightly as if they'd saved up their best work for these final episodes, and had teased us with last week's storylines and suggestions of hope, only to dash them almost straight away. Certainly my feelings about Birgitte changed very rapidly. But then I suppose we're watching what would have unfolded over two weeks in one chunk. And it was very well done: the parallels between Birgitte and Katrine – both initially principled women determined to fight for their ideals – were pointed up throughout. (Admittedly, as with the "doing other people's jobs" storyline sometimes a little heavily.) But their end points told a different story: Birgitte, still in her job but compromised; Katrine unemployed but as idealistic as ever.

(Although I do wonder: if Katrine decided to spill the beans on why she resigned from Denmark's main broadcaster, it could be Birgitte who finds herself out of a job. Certainly such a story would have caused major scandal in the UK. As, of course, would Birgitte busting into Freja's apartment.)

It was strange, too, to feel anything like sympathy for a spouse who falls straight into the arms of the nearest headhunter when the going gets tough. But oddly, despite his indefensible betrayal, I did. Below the line last week, there was rightly an entire lack of patience for Philip and his inability to support Birgitte. And really, he didn't waste any time embarking on an affair. But as Birgitte's paranoia and tunnel vision grew stronger, to me her demands became ever less defensible.

Surely she could have ridden out any media storm around Philip's job? It felt like a massive over-reaction on Birgitte's part over something that was easy to explain and completely free of corruption. And she did not question for a second that Philip should sacrifice his job for hers. She even got Kasper to draft the release. Last week's episodes left me thinking that Philip needed to get over his status problems and need to be as powerful as his wife. This week my sympathies shifted significantly as Birgitte bossed him into resigning and tried to capitalise politically on their relationship.

It was interesting too that as the series progressed, it seemed to move away from traditional questions about women and work and family and balance, and into a far more nuanced examination of the dynamics of ambition and power within a relationship and the effects of that. (Commenter @mb44 had an interesting take on this last week.) I found that rather impressive.

For me the bleakest moment came, without doubt, as Philip and Birgitte sat stiffly around their unusually tidy, quiet table and talked about their future. Not only had Birgitte become every inch the professional politician she had spoken out against before election, but she had also brought that professionalism into the family home: attempting to cut a deal so she could save face and have an almost happy homelife. Even Philip – basically being given licence to sleep with whomever he chose and keep his home life – looked appalled. Not that it stopped him from organising some "meetings". Really.

The kids were also good in this double bill, Laura in particular reminding us (and sometimes Birgitte, it seemed) that the grown-ups' actions affected more people than just them. It's been interesting in fact how underplayed the kids have been: we've had Magnus and the school psychologist and a couple of looks from Laura, but none of the really heartbreaking stuff it must have been tempting to put on screen.

It did, however, feel something of a shame that after the reveal about Kasper's childhood last week, that the whole area of discussion was effectively shut down again: Katrine still doesn't know the full truth, and Kasper apparently can't tell her. Instead he was off trying to shag lovely Sanne – who seriously had the most appalling week ever: dumped and then fired – when really, he was still pining for Katrine. (Well, that's my reading of it at least: helping to get her job back, petrified of what she would think if she knew the strings attached, etc.)

Talking of which… While I really liked the mini expenses scandal storyline with Theis, sorry, Thorsen, heading off for lovely grouse-shooting holiday and taking receipt of some £25,000 guns (really?), I'm not sure I entirely bought the idea that Torben would have given Kasper complete editorial control – and indeed a veto – on a report. In fact, I slightly stopped buying Torben as a character these episodes – journalists who worry about being told off and getting into trouble? Who say yes to everything the prime minister wants? Even though he was presented as a management lackey, Friis would surely have had more backbone than that. It was the only duff note in a newsroom that was otherwise rather well drawn.

Thoughts and observations

• Good news! Borgen is coming back for a second series on BBC4. Bad news! Not until next winter.

• I spent quite a lot of this double bill wondering whether Birgitte had any friends at all beyond Bent. No girlfriends to confide in? Although I did love Bent's bossy advice: "Come to an agreement – and eat your roll".

• Birgitte told Bent: "I did what is necessary. That's what a prime minister does." Perhaps. But not what a friend does.

• And finally … a massive thank you for all your comments. It's been a real pleasure to read your contributions, and I've enjoyed watching the show with you. BBC4 is going to take a short break from Scandi drama – although Montalbano fans rejoice as the Sicilian detective returns to Saturday nights – but I imagine we'll be back in the spring when The Bridge airs. See you then. Tak skal du have!